System and method for chemical mechanical polishing

ABSTRACT

A chemical mechanical polishing machine includes a spindle operable to rotate with respect to a central axis. A wafer carrier may be coupled with the spindle, the wafer carrier operable to rotate in response to rotation of the spindle. A substrate may be coupled with the wafer carrier. In accordance with a particular embodiment of the present invention, a plurality of piezoelectric drive elements may be coupled with the wafer carrier.

RELATED APPLICATIONS

[0001] The present invention is related to pending patent applications U.S. Ser. No. 09/014,202 filed Jan. 28, 1998, entitled Active Planarity Control Mechanism for CMP, by Jeffrey L. Large, and U.S. Ser. No. 60/081,111 filed Apr. 8, 1998, entitled Chemical Management Polishing Machine with Ultrasonic Vibration and Method, by McKee, et al.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates generally to silicon wafer processing and more particularly, to a method and system for chemical mechanical polishing incorporating a piezoelectric drive element.

BACKGROUND OF THE INVENTION

[0003] Chemical mechanical polishing (“CMP”) is a silicon wafer flattening and polishing procedure widely used in the fabrication of silicon wafers. CMP is used for polishing and/or flattening wafers after crystal growing, slicing, and wafer planarization, during the wafer fabrication process. As the name implies, there are two components to the process; chemical and mechanical polishing. Chemical polishing involves the introduction of chemicals that dissolve imperfections and impurities present upon the wafer. Mechanical polishing involves rotating the wafer upon an abrasive platen in order to grind the wafer to a predetermined thickness.

[0004] The wafers are mounted upside down on a holder and rotated above a pad sitting on a platen. The platen is also rotated. Typically, a slurry containing both chemicals and abrasives is introduced upon the platen.

SUMMARY OF THE INVENTION

[0005] The present invention provides a system and method for chemical mechanical polishing that substantially eliminates or reduces the problems and disadvantages associated with the previous methods and systems. In particular, a piezoelectric drive is incorporated into a CMP machine in order to induce microscopic vibration into the chemical mechanical polishing process, at specific, predetermined locations upon a silicon wafer. The piezoelectric drive provides dynamic pressure points to the silicon wafer, and increases the temperature at specific areas upon the wafer in order to enhance the chemical reactions taking place.

[0006] In accordance with a particular embodiment of the present invention, a substrate having a plurality of piezoelectric drive elements coupled thereto, is provided. The piezoelectric drive elements are operable to cooperate with a silicon wafer to impart forces to predetermined locations upon the silicon wafer.

[0007] In accordance with another embodiment, the substrate is coupled with a wafer carrier. The wafer carrier may be coupled with a spindle operable to rotate with respect to a central axis. Accordingly, the wafer is operable to rotate in response to rotation of the spindle.

[0008] The teachings of the present invention provide a solid state CMP device with high mechanical stability and reliability. The piezoelectric drive provides a method of introducing forces into the CMP process in precise, predetermined locations and directions. Slurry etch rates are also increased and controllable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a more complete understanding of the present invention and its advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, in which:

[0010]FIG. 1 is a diagrammatic plan view of a chemical mechanical polishing machine, in accordance with one aspect of the present invention;

[0011]FIG. 2 is a diagrammatic view from above, with portions broken away, illustrating the CMP machine of FIG. 1;

[0012]FIG. 3 is an isometric exploded view, with portions broken away, illustrating the CMP machine of FIG. 1;

[0013]FIG. 4A is an isometric view illustrating the piezoelectric drive of FIG. 3;

[0014]FIG. 4B is a cross section taken through 4B-4B of FIG. 4A;

[0015]FIG. 5A is an isometric view illustrating a piezoelectric drive, in accordance with another embodiment of the present invention; and

[0016]FIG. 5B is a cross section taken through 5B-5B of FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The preferred embodiments of the present invention and its advantages are best understood by referring now in more detail to FIGS. 1-5B of the drawings, in which like numerals refer to like parts.

[0018]FIG. 1 is a diagrammatic plan view, with portions broken away, illustrating a chemical, mechanical polishing (“CMP”) machine incorporating aspects of the present invention. CMP machine 30 includes a wafer holder 32 having a plurality of spindles 34 extending therefrom. Each spindle 34 is coupled with wafer holder 32 at a first end 36. A wafer carrier 38 is coupled with each spindle 34 at a second end 37 of each spindle 34. A platen 40 is disposed adjacent the wafer carriers 38, along a plane approximately perpendicular to a central axis of rotation of spindle 34. A polishing pad 42 is coupled with platen 40 and disposed between wafer carriers 38 and platen 40.

[0019] CMP machine 30 may be used for polishing and/or flattening silicon wafer crystals after growing, slicing and wafer planarization, during the silicon wafer fabrication process. In the illustrated embodiment, silicon wafers may be coupled with one or more wafer chucks, or wafer carriers 38. Each wafer carrier 38 is configured to rotate in response to rotation of spindle 34. Platen 40 is configured to rotate during the polishing process, in the same direction as the direction of rotation of spindle 34 and wafer carrier 38. Accordingly, wafer carrier 38 causes the silicon wafer to contact polishing pad 42. The rotation of wafer carrier 38 and/or polishing pad 42 polish and grind the silicon wafer to provide a clean, flat surfaces on the silicon wafer(s).

[0020] A liquid slurry delivery system 19 provides a liquid slurry to polishing pad 42, to enhance the polishing process. The liquid slurry may include acids, and other chemicals which interact with the silicon wafer in order to loosen, and at least partially remove metals, oxidation, and other impurities present upon the silicon wafer. The liquid slurry may also include small particles of glass, and/or other abrasive materials. These abrasive materials grind the silicon wafer in response to rotation of wafer carrier 38 and polishing pad 42, during the polishing process.

[0021]FIG. 2 is a diagrammatic view from above, with portions broken away, illustrating portions of CMP machine 30 of FIG. 1. As illustrated in FIG. 2, CMP machine 30 includes four (4) wafer carriers 38. Each wafer carrier 38 is associated with a particular polishing station. Accordingly, four (4) silicon wafers may be polished simultaneously using CMP machine 30. Also, in a particular embodiment, each silicon wafer may be polished using each of the four (4) polishing stations, and therefore each of the four (4) wafer carriers 38, at different stages of the polishing process. In this manner, each silicon wafer may be exposed to four (4) separate and distinct polishing processes, using CMP machine 30, and each polishing process and/or each wafer carrier 38 may be configured differently in order to provide various grades and degrees of grinding and/or polishing of the silicon wafer.

[0022] In the illustrated embodiment of FIG. 2, platen 40, and therefore, polishing pad 42 rotate in a counter clockwise direction as indicated by directional arrow 44. In this embodiment, each wafer carrier 38 may be configured to rotate in an opposite direction, or clockwise. Alternatively, one or more of the wafer carriers 38 may be configured to rotate counterclockwise, in the same direction as platen 40 and polishing pad 42. Various design characteristics, and the particular goals of the operator of CMP machine 30 may be considered in order to determine the appropriate direction of rotation 44 of platen 40, polishing pad 42, and each independent wafer carrier 38.

[0023]FIG. 3 is a diagrammatic perspective view, with portions broken away, illustrating CMP machine 30 of FIG. 1. Portions of CMP machine 30 of FIG. 3 are illustrated in an exploded manner, for purposes of clarity.

[0024] Referring to FIG. 3, spindle 34 is illustrated and includes a wafer carrier 38 coupled at a second end 37 of spindle 34. A piezoelectric drive 46 which is coupled with wafer carrier 38, is illustrated in the exploded view. Piezoelectric drive 46 is also coupled with drive electronics 48. Drive electronics 48 provide electronic signals to piezoelectric drive 46 using a pair of leads 50 and 52. Drive 46 has the ability to generate mechanical force when a voltage is applied. In a particular embodiment, drive 46 may include piezoelectric ceramic, which will change shape, thereby exerting a mechanical force, in response to a voltage. Piezoelectric drive 46 and drive electronics 48 will be described later in more detail with regard to FIGS. 4A-5B.

[0025] In the illustrated embodiment, leads 50 and 52 include contacts which couple leads 50 and 52 with drive 46. The contacts remain stationary and maintain contact with drive 46 while drive 46 is rotating. In another embodiment, the contacts may be attached to the drive such that the contacts rotate along with drive 46. One way to accomplish this is to couple drive electronics 48 with wafer carrier 38, spindle 34, or other component which is rotating at the same rate as drive 46.

[0026] A rubber adhesion pad 54, which may be coupled with wafer carrier 38 and/or piezoelectric drive 46, is illustrated in FIG. 3. Adhesion pad 54 includes a plurality of vacuum holes 56 which may be used in conjunction with a vacuum device associated with wafer carrier 38, in order to couple a silicon wafer with adhesion pad 54 and/or wafer carrier 38. Rubber adhesion pad 54 is an optional component, provided in the illustrated embodiment to allow a smooth transition between piezoelectric drive 46 and silicon wafer 58. Silicon wafer 58 may be coupled with rubber adhesion pad 54, piezoelectric drive 46 and/or wafer carrier 38, is illustrated in FIG. 3. Silicon wafer 58 is an example of the type of silicon wafer which may be polished, flattened, and otherwise processed using CMP machine 30. In the illustrated embodiment of FIG. 3, silicon wafer 58 is a thin, circular disk configuration. Silicon wafers of various sizes, shapes and configurations may be processed using CMP machine 30.

[0027] The portions of CMP machine 30 illustrated in FIG. 3 are shown to illustrate the type of CMP equipment which may incorporate aspects of the present invention. Various other CMP equipment is available for use within the teachings of the present invention. For example, the Mirra Mesa chemical mechanical polishing machine, as manufactured by Applied Materials may be used within the teachings of the present invention. It will be recognized by those of ordinary skill in the art that the type of CMP machine, along with the size, shape and configuration of the various components illustrated including, without limitation, spindle 34, wafer carrier 38, piezoelectric drive 46, rubber adhesion pad 54, silicon wafer 58, platen 40 and/or polishing pad 42 may be varied significantly within the teachings of the present invention.

[0028] In the embodiment illustrated in FIG. 3, piezoelectric drive 46 is disposed between wafer carrier 38 and wafer 58. In practice, drive 46 may be placed practically anywhere on CMP 30. For example, drive 46 may be coupled with platen 40 and force may be delivered to wafer 58 through platen 40 and/or polishing pad 42. Alternatively, drive 46 may be located above spindle 34 and force may be transferred to wafer 58 through spindle 34. The location of drive 46 of FIG. 3 is selected because its proximity to wafer 58 avoids the dissipation of energy prior to reaching wafer 58.

[0029] The piezoelectric drive 46 of FIG. 3 is configured to provide a force upon silicon wafer 58 in a direction approximately parallel to central axis 41. Central axis 41 is approximately perpendicular to the axis of rotation of platen 40. In another embodiment, drive 46 may be configured to apply a force upon wafer 58 in a direction(s) approximately perpendicular to axis 41. The teachings of the present invention may be used to provide a force to wafer 58 in practically any direction or directions (x,y,z coordinates). This helps local planarization by providing mechanical force vectors, or dynamic pressure points, to the wafer planarization process.

[0030] Piezoelectric drive 46 will also enhance the chemical reactions used to remove impurities from wafer 58. During operation, the piezoelectric effect is exothermic, which will enhance the environment of the chemical reaction by raising the temperature.

[0031]FIG. 4A is a diagrammatic perspective view illustrating piezoelectric drive 46 in more detail. Piezoelectric drive 46 includes a substrate 60 coupled with a plurality of piezoelectric drive elements 62-67. Piezoelectric drive element 62 is generally a circular disk configuration, having an axial midpoint 70. Each of piezoelectric drive elements 63-67 include circular-ring shaped concentric structures, of increasing diameter, which generally share a common midpoint 70 with piezoelectric drive element 62. The size, shape and configuration of each piezoelectric drive element 62-67 may be significantly altered within the teachings of the present invention.

[0032] Substrate 60 cooperates with each piezoelectric drive element 62-67 and provides an independent interface with each piezoelectric drive element 62-67. In a particular embodiment, the interface between substrate 60 and each of piezoelectric drive elements 62-67 may include an independent pair of electrical leads to each of piezoelectric drive elements 62-67. Accordingly, each piezoelectric drive element 62-67 may be coupled with one or more frequency generators 72 (FIG. 3), in order to provide independent electrical signals to each of piezoelectric drive element 62-67.

[0033] In an alternative embodiment, one or more of piezoelectric drive elements 62-67 may be omitted from substrate 60. Therefore, a void may be provided between one or more adjacent piezoelectric drive elements 62-67. Alternatively, a non-piezoelectric structure may be used in lieu of one or more of piezoelectric drive elements 62-67. Such non-piezoelectric structures would provide a “dead” space between adjacent remaining piezoelectric drive elements 62-67.

[0034] As previously discussed, in the illustrated embodiment, each piezoelectric drive element 62-67 is coupled with a respective frequency generator 72. An amplifier 74 may also be provided and coupled with frequency generator 72 in order to enhance electrical signals travelling between frequency generator 72 and drive electronics 48.

[0035] Frequency generator 72 may include any one of various tunable wave-form generators which provide an operator with the ability to modulate frequency and/or amplitude of the electrical signals provided to piezoelectric drive 46. Accordingly, piezoelectric drive 46 provides tunable, acoustic energy to the chemical mechanical polishing process utilizing CMP machine 30. The acoustic energy determines the direction and amount of force applied to the silicon wafer. Each independent piezoelectric drive element 62-67 allows an operator to add a variable controllable amount of energy to the chemical mechanical polishing system and exploit energies of specific frequencies. Frequencies available for use within the teachings of the present invention include, without limitation, sonic, ultrasonic and supersonic.

[0036] Since each piezoelectric drive element 62-67 may operate independently of the others, piezoelectric drive 46 also provides the operator of CMP machine 30 with the ability to pinpoint forces associated with the acoustic energy to particular locations upon a silicon wafer. Piezoelectric drive elements 62-67 provide microscopic motion (vibration) to the polishing process.

[0037] In a particular embodiment, a measurement system associated with CMP machine 30 can take various measurements, including without limitation thickness and planarity, of silicon wafer 54, before, during and after processing. This allows the operator to selectively adjust the amount of energy supplied to any given piezoelectric drive element 62-67 based upon its location upon piezoelectric drive 46. For example, if an operator determines that silicon wafer 58 is thicker at its edges adjacent piezoelectric drive element 67, the operator may provide additional energy to piezoelectric drive element 67 compared to the amount of energy provided to elements 62-66. Accordingly, the additional energy supplied to piezoelectric drive element 67 will translate into a greater force in a direction approximately parallel to the central axis of spindle 34. Additional energy may be supplied to piezoelectric drive element 67 until the measurement system associated with CMP machine 30 determines that the irregular edge condition has been corrected.

[0038] Referring to FIGS. 4A and 4B, the concentric circle configuration of piezoelectric drive elements 62-67 is beneficial since it corresponds with the circular disk shape of silicon wafer 58. For most applications, the operator of CMP machine 30 will be interested in achieving a completely flat planar surface across silicon wafer 58. Accordingly, the introduction of energy to any of piezoelectric drive elements 62-67 will enhance grinding and polishing operations over the entire circular-ring shaped region of silicon wafer 58, adjacent the particular piezoelectric drive element 62-67. In the illustrated embodiment, six piezoelectric drive elements 62-67 are illustrated for purposes of clarity. It will be recognized by those of ordinary skill in the art that the number, size, shape and configuration of piezoelectric drive elements 62-67 may be significantly varied within the teachings of the present invention.

[0039] In general, the accuracy and precision with which energy and force may be provided to piezoelectric drive 46, and transferred to silicon wafer 58 will increase proportionally to the number of piezoelectric drive elements 62-67. In practice, practically any number of piezoelectric drive elements may be provided upon substrate 60, within the teachings of the present invention.

[0040] As previously discussed, each piezoelectric drive element 62-67 is arranged in concentric rings, and each drive element includes an independent control system having a frequency generator. This system may incorporate “fixed” control variation from center to edge to correct known uniformity variations of the film to be polished, or CMP polisher characteristics. Additionally, the control may be based on feedback from an endpoint detection system (such as the MIRRA ISRM, provided by Applied Materials) to continuously vary the piezoelectric drive elements 62-67 to correct non-uniformities as they develop during wafer polishing.

[0041]FIG. 5A is a diagrammatic perspective view illustrating an alternative embodiment piezoelectric drive 146, in accordance with a particular aspect of the present invention. Piezoelectric drive 146 includes a plurality of piezoelectric drive elements 162-173, arranged in a grid-like fashion upon a substrate 160. Piezoelectric drive elements 162-163 may be provided in various geometric configurations. For example, in the embodiment illustrated in FIG. 5A piezoelectric drive elements 165-170 generally conform to rectangular configurations. Piezoelectric drive elements 162-164, 167-168 and 171-173 are approximately right triangular configurations, although each includes a hypotenuse formed by the arc of a circle.

[0042] Referring to FIGS. 5A and 5B, each piezoelectric drive element 162-173 defines a region upon piezoelectric drive 146 in which energy may be focused, in order to provide a force upon adjacent components (i.e. a silicon wafer). Accordingly, similar to piezoelectric drive 46, an operator of piezoelectric drive 146 has the ability to focus energy and therefore forces upon specific locations or regions of a silicon wafer during polishing, in order to correct imperfections, as required. Similarly, an automatic measurement system associated with CMP 30 of FIG. 1 may be used to measure a silicon wafer and detect imperfections. The measurement system may be used to determine the appropriate distribution of energy amongst piezoelectric drive elements 162-173 to achieve a predetermined width, and/or flatness upon the silicon wafer.

[0043] In a particular embodiment of the present invention, any one or more of piezoelectric drive elements 162-173 may be omitted from piezoelectric drive 146 and/or replaced with a non-piezoelectric material. In practice, however, more piezoelectric drive elements upon any piezoelectric drive will provide an operator with a greater degree of pinpoint accuracy for the direction of energy and forces within the polishing system.

[0044] Piezoelectric drive 146 of FIG. 5A includes a central axis 147. Piezoelectric drive 146 has two sides 148 and 149, each of which comprise approximately half of overall piezoelectric drive 146. In the illustrated embodiment of FIG. 5A, sides 148 and 149 are generally mirrored images of one another. Accordingly, generally uniform, central cross-sections are provided. Therefore, an operator of CMP machine 30 may introduce energy into piezoelectric drive 146 in a standard grid pattern.

[0045] As previously discussed, the piezoelectric effect is exothermic and heat will be released during the operation of drives 46 and 146. This may be used to enhance the efficiency of the wafer polishing process by concentrating piezoelectric energy at predetermined locations on wafer 58. Localized energy will increase the temperature and enhance the chemical reactions occurring at those specific locations. The operator and/or CMP machine 30 may incorporate a device that measures properties of wafer 58, including without limitation thickness, reflectivity, resistivity and refractive index at specific locations. This information may be used to determine the appropriate locations upon wafer 58 to provide piezoelectric energy, and therefore, localized heating.

[0046] It will be recognized by those of ordinary skill in the art that various configurations of piezoelectric drive elements upon a substrate may be utilized within the teachings of the present invention. In the embodiments illustrated in FIGS. 4A-5B, concentric circle, rectangular and approximate triangular configurations were disclosed. Various other configurations may include star patterns, flower petal configurations and/or cross-configurations. 

What is claimed is:
 1. An apparatus, comprising: a substrate; and a plurality of piezoelectric drive elements coupled with the substrate, the piezoelectric drive elements operable to cooperate with a silicon wafer to impart forces at predetermined locations upon the silicon wafer.
 2. The apparatus of claim 1, wherein at least two of the plurality of piezoelectric drive elements share a common central axis.
 3. The apparatus of claim 1, wherein at least two of the plurality of piezoelectric drive elements include approximately circular-ring cross sections, and share a common central axis.
 4. The apparatus of claim 1, further comprising a first half and a second half, wherein the second half is approximately a mirrored image of the first half.
 5. The apparatus of claim 1, wherein each of the plurality of piezoelectric drive elements include respective first and second electrical contacts.
 6. The apparatus of claim 5, wherein the first and second electrical contacts associated with each piezoelectric drive element are operable to couple their respective piezoelectric drive elements with independent frequency generators.
 7. An apparatus, comprising: a spindle operable to rotate with respect to a central axis; a wafer carrier coupled with the spindle, the wafer carrier operable to rotate in response to rotation of the spindle; a substrate coupled with the wafer carrier; and a plurality of piezoelectric drive elements coupled with the wafer carrier.
 8. The apparatus of claim 7, wherein the wafer carrier is adapted to receive a silicon wafer.
 9. The apparatus of claim 7, further comprising: a structural arm coupled with the spindle; a rotating platen disposed adjacent the wafer carrier; and wherein the structural arm is operable to maintain the wafer carrier within a predetermined distance from the platen.
 10. The apparatus of claim 7, further comprising liquid delivery dispenser operable to provide a fluid to the platen.
 11. The apparatus of claim 7, wherein the piezoelectric drive elements are operable to impart forces upon the wafer carrier in a direction approximately parallel to the central axis.
 12. The apparatus of claim 7, wherein the piezoelectric drive elements are operable to impart forces upon a wafer coupled with the wafer carrier along a plane approximately perpendicular to the central axis.
 13. The apparatus of claim 7, wherein the wafer carrier includes a rubber mounting pad, configured to receive a silicon wafer.
 14. The apparatus of claim 7, further comprising drive electronics electrically coupled with one or more of the piezoelectric drive elements and operable to provide electrical signals to the piezoelectric drive element.
 15. A method for polishing a silicon wafer, comprising: coupling the silicon wafer with a wafer carrier; coupling the wafer carrier with a plurality of piezoelectric drive elements: coupling each of the piezoelectric drive elements with respective frequency generators; and rotating the wafer carrier with respect to a platen, wherein the silicon wafer is disposed between the wafer carrier and the platen.
 16. The method of claim 15, further comprising providing a fluid solution to the platen.
 17. The method of claim 15, further comprising rotating the platen with respect to a central axis of the wafer carrier in a direction opposite a direction of rotation of the wafer carrier.
 18. The method of claim 15, further comprising configuring the piezoelectric drive elements to impart forces upon the silicon wafer in a direction approximately perpendicular to a central axis of the wafer carrier.
 19. The method of claim 15, further comprising configuring the piezoelectric drive elements to impart forces upon the silicon wafer in a direction approximately parallel to a central axis of the wafer carrier.
 20. A method for forming a piezoelectric drive, comprising: coupling a plurality of piezoelectric drive elements with a substrate; and selecting the location of the piezoelectric drive elements to impart forces upon a silicon wafer, in response to contact with the silicon wafer, at predetermined locations upon the silicon wafer.
 21. The method of claim 20, further comprising configuring the piezoelectric drive elements such that at least two of the piezoelectric drive elements share a common central axis. 